1. Field of the Invention
The present invention relates to a polyol, polyurethane resin, rigid polyurethane foam, preparation process thereof and a preparation process of a rigid polyurethane foam composite.
More particularly the polyol mixture of the present invention comprising an epoxy resin based polyol and a polyol component initiated with a single compound or a mixture thereof selected from phenol resin, aliphatic polyhydroxy compound, alkanolamine and aromatic amine is a raw material for preparing polyurethane resin having resistance to dissolution in hydrochlorofluorocarbons (hereinafter abbreviated as HCFC) and hydrofluorocarbons (hereinafter abbreviated as HFC) which are foaming agents causing very low public hazards. The polyol can provide rigid polyurethane foam and its composites thereof by using the above foaming agents.
The rigid polyurethane foam among them obtained above has excellent properties equivalent to those of conventional polyurethane foams obtained by the use of chlorofluorocarbons (hereinafter abbreviated as CFC) as foaming agents. Hence, the rigid polyurethane foam of the present invention is extremely useful for insulating materials or insulating structural materials of electric refrigerators, freezing warehouses, insulation panels, ships and vehicles.
2. Description of the Prior Art
In the present manufacturing process of polyurethane foams, CFC such as CFC-11 (trichlorofluoromethane) and CFC-12 (dichlorodifluoromethane) are generally used as foaming agents. These compounds have recently been recognized as materials causing environmental destruction such as disruption of the ozone layer or enhancement of the greenhouse effect. Accordingly, restriction has recently been imposed upon the manufacture and use of these compounds.
At the same time, HCFC such as HCFC-123 (2,2-dichloro-1,1,1-trifuluoroethane), HCFC-141b (1,1-dichloro-1-fluoroethane) HCFC-142b(1-chloro-1,1-difluoroethane), HCFC-22(1-chloro-1,1-difluoromethane) and additionally HFC such as HFC-134a (1,1,1,2-tetrafluoroethane) and HFC-152a (1,1-difluoroethane) which cause much less environmental destruction have been focused on as substitutes for CFC-11 and CFC-12 and the like. However, it was found that HCFC and HFC have higher dissolving powers for rigid polyurethane resins as compared with CFC, and hence have disadvantages of severely deteriorating the properties of the resulting rigid polyurethane foams, for example, reduction of closed cell content and foam strengths. Particularly it has been confirmed by the present inventors that in the manufacture of rigid polyurethane foams, HCFC and HFC dissolve the cell walls of closed cells in the course of foaming and drastically lower the heat insulation effect which is a characteristic property of rigid polyurethane foams.
Consequently, a novel polyurethane resin has been desired. The conventional polyoxyalkylene polyol (hereinafter abbreviated as polyol) used as the raw material for polyurethane resins decreases viscosity according to an increase in the amount of alkylene oxide added. As a result, operations in polyurethane resin production can be conducted with ease. However, excess addition of alkylene oxide leads to dissolution of polyurethane resin in HCFC and HFC, and tends to made application of these foaming agents substantially impossible. On the other hand, when the amount of alkylene oxide added is reduced, the polyol becomes solid or extremely viscous and solubility of polyol in other raw materials becomes poor. Thus the polyol is very difficult to handle.
As mentioned above, in order to maintain resistance to dissolution in HCFC and HCF, the operational efficiency in the rigid polyurethane foam production must be greatly sacrificed. Polyol which has a viscosity suitable for the foaming operation, good resistance to dissolution in HCFC and HFC and which is excellent in the mixing and dispersing ability in HCFC and HFC has never been found.
Tokkai-Sho 50-6698 (1975) has disclosed polyurethane foam which has good resistance to high temperatures using epoxy resin, polyol having hydroxyl value of from 300 to 550 mgKOH/g and CFC as the foaming agent.
Tokkai-Sho 63-139908 (1988) has disclosed an epoxy resin modified polyol having a molecular weight of from 2000 to 7000 and a flexible polyurethane foam for packing using CFC and low boiling point hydrocarbon as the foaming agent.
Tokkai-Hei 2-86613 (1990) has disclosed a flexible polyurethane foam using modified polyol obtained by reacting epoxy resin with polyamine or dialkanolamine in a polyol, which is subsequently reacted with organic polyisocyanate.